Nitric Oxide (NO) is an essential signaling molecule for diverse physiological and disease processes. While the regulation of NO flux has focused primarily on the study of the three NO synthases (NOS), their respective genetic deficiencies exhibit relatively modest phenotypes. This has led to difficulties in dissecting the specific cellular contributions to NO in different disease processes. In contrast, the hypothesized intracellular compartmentalized availability of arginine substrate in specifying NO flux may explain the arginine paradox. In humans, the natural history of urea cycle disorders and specifically of argininosuccinic aciduria (ASA) caused by deficiency of argininosuccinic acid lyase (ASL) shows systemic and chronic features that may reflect global dysregulation of NO homeostasis. We propose that ASL is in fact the central regulator of NO homeostasis because it is essential for both the intracellular production of arginine and the utilization of extracellular arginine. In preliminary data, we identify a distinct subcellular and biochemical compartment where local cellular arginine production and channeling by ASL regulates systemic NO production. We have generated a conditional genetic model of Asl deficiency that will allow us to study the consequences of cell autonomous loss of NO in brain (neurons vs. glial cells), the cardiovascular system (endothelial vs. smooth muscle cells), and the pancreatic beta cell with broad implications on understanding the contribution of NO to models of neurodegeneration, cardiovascular disease, and metabolic syndrome. On a biochemical level, we will assess how ASL controls arginine availability for NO production. Our studies may identify novel and more effective strategies for manipulation NO in multi-system disease.